EVIDENCE FOR POST-EXERCISE STUNNING IN PATIENTS WITH ABNORMAL LUNG:HEART RATIO BY GATED THALLIUM SPECT: In this study, we hypothesized that patients with abnormal lung uptake of thallium during exercise are more likely to develop post-exercise persistent left ventricular (LV) dysfunction (stunning) than those with normal lung:heart (L/H) ratio. To this end, we examined global LV ejection fraction (EF) derived from gated post-exercise and gated reinjection thallium SPECT in 52 patients undergoing stress-redistribution-reinjection thallium for evaluation of coronary artery disease using a 3-headed SPECT camera. Acquisitions were gated for 10 frames per cardiac cycle. LVEF was computed applying a recently developed and validated algorithm for gated perfusion studies that is based on the epicardial contour of the myocardium. Stress perfusion defects were assessed in 5 myocardial regions per patient (anterior, septal, apical, inferior and lateral). Thallium L/H ratios were assessed from the anterior projections and L/H ratio <50% was considered abnormal. Of the 52 patients studied, 11 showed abnormal L/H ratio of <50%. Among the 11 patients with abnormal L/H ratio, mean post-exercise LVEF was lower (51+14%) when compared to LVEF computed from reinjection images 3-4 hours after stress (58+13%, p<0.05). In contrast, among the 41 patients with normal L/H ratio, mean LVEF (75+19%) did not decrease post-exercise when compared to reinjection LVEF (70+20%, p<0.05). The number of stress-induced thallium defects was significantly higher in patients with abnormal L/H ratio (mean 2.5/patient) when compared to those with normal L/H ratio (mean 1.2/patient, p<0.001). Of the 11 patients with abnormal L/H ratio, 9 (82%) exhibited thallium perfusion defects in at least 2 myocardial regions on stress compared to 14 of 41 (34%) patients with normal L/H ratio (p<0.007). In patients with abnormally increased L/H ratio on stress thallium, LVEF derived from post-exercise thallium SPECT may reflect persistent ischemic LV dysfunction (stunning) and thereby overestimate the severity of LV dysfunction. Because thallium reinjection images are acquired 3-4 hours after stress, LVEF derived from reinjection thallium SPECT may more accurately reflect LV function in such patients.